The present invention relates to night vision systems, and particularly concerns a color-corrected laser illumination system for night vision applications.
Conventional lighting systems used in automotive vehicle applications such as headlights and taillights utilize an incandescent bulb with a reflector. The light emitted by the incandescent bulb is generally collimated by the reflector. The incandescent bulb is used to generate light in the visible spectrum for headlight and taillight applications. Active night vision systems typically require near-infrared emission that is compatible with solid-state CCD or CMOS cameras to illuminate the region forward of the vehicle.
Advances in solid-state lasers have given rise to thin-sheet lighting systems for use in taillight and active night vision systems. The thin sheet systems require less space than bulb and reflector systems. Furthermore, laser diodes are more energy efficient and reliable than incandescent bulbs. A challenge in thin-sheet lighting systems is to rapidly spread the laser light over a sufficiently wide area to meet spatial illumination requirements for good visibility and, at the same time, eye safety requirements as mandated under laws governing such applications.
U.S. Pat. No. 6,422,713 issued Jul. 23, 2002 and entitled “Thin-Sheet Collimation Optics For Diode Laser illumination Systems For Use In Night Vision And Exterior Lighting Applications” describes thin-sheet collimation optics which can be used to produce eye-safe, diode laser-based headlamps for night vision applications. The emission patterns of optics such as disclosed in the referenced application are similar to those of “high-beam” headlamps in that they project far forward to illuminate objects at long range and also provide spread-light for illuminating objects at close range on either side of the vehicle.
For most night vision applications, the laser emission wavelength is typically in the near infrared range (800–900 nm), for example, 810 nm which is outside the spectrum of light normally considered to be visible to the human eye (400–750 nm). Moreover, although the human eye is extremely insensitive to near infrared light, it may be possible under certain conditions for a driver to perceive a near infrared night vision laser headlamp of an approaching vehicle as a dim red light. Current government guidelines prohibit the use by a non-law-enforcement or non-emergency vehicle of any forward lighting device that could be perceived as “red” by other vehicle operators. Thus, there exists a need for “color-corrected” laser headlamps for night vision applications that could not be perceived as red light by other vehicle operators.